1. Field of the Invention
The present invention relates in general to a two-axis ball-based cursor control apparatus, such as a mouse or trackball, and in particular to a cursor control apparatus incorporating a helical screw mechanism for measuring the rotational displacement of the ball, in order to minimize the overall size of the cursor control apparatus.
2. Background Art
Two-axis cursor control devices are well-known in the art. These types of devices are common components of personal computer systems used for controlling the movement of a cursor appearing on a video monitor. Cursor control devices are also finding use in handheld devices such as PDA's and cellular telephones where graphical user interfaces are manipulated by the user in operating the device. Two well-known forms of such devices include the computer mouse and the trackball. A computer mouse consists of a spherical ball, generally approximately one-half inch in diameter and freely rotatable about two axes of rotation, mounted within a larger housing which rests on a flat surface, so that a portion of the ball protrudes from the bottom of the housing and comes into contact with the surface. Typically, a pair of rotors come into contact with the ball, one aligned with each axis. Each of these rotors are in turn connected by an axle to a disk with uniformly spaced slots or holes spaced around the outer portion thereof. When the mouse is moved along the flat surface, the rotation of the ball is translated to the rotors, and in turn to the associated disks. Light emitters and sensors are positioned spanning each of the disks whereby the beam of light is alternatively passed through the disk to the sensors and then blocked from the sensors as the disk rotates. Each disk typically has two pairs of emitters and sensors associated therewith in order to determine the rate and direction of rotation of the disk. The sensors are connected to an electrical circuit which generates an electrical signal. From the signals generated by each of the two disks positioned perpendicular to one another, the direction and acceleration of the displacement of the ball, and hence of the mouse itself, is determined. This information is then translated into motion of a cursor on the screen of the computer using a predetermined relationship between the magnitude of the mouse displacement in each direction and the distance which the cursor moves in that direction. Thus, the user's horizontal and vertical movement of the mouse on the flat surface is translated into horizontal and vertical movement of the cursor on the screen.
A trackball is a similar type of cursor control apparatus in which the user merely rotates the ball itself instead of moving the entire housing. The ball typically protrudes from the top of its housing, where it can be rotated directly by the user by hand. The remainder of the device is typically substantially similar to that described above, with the rotation of the ball translated to a pair of rotors associated with each axis of rotation, and then to a pair of disks, whose motion is then translated into cursor motion by light sensors. Thus, unlike a mouse, a trackball apparatus remains stationary while the user directly rotates the ball itself.
One significant disadvantage of such prior art construction of such devices is its overall size. A computer mouse typically measures several inches in length and width and approximately an inch in height, and a typical trackball apparatus is generally even larger. One constraint on the size of such cursor control devices is the size of the disks associated with the light emitters and sensors. A disk must have a minimum number of slots or holes to generate a sufficient number of pulses in a signal for the mouse to be useable. The number of slots or holes in the disk correspond to the resolution of the mouse. For example, a disk with only four slots or holes will generate four pulses for each rotation of the axle as driven by the roller and in turn the ball. However, any movement of less than a quarter turn of the axle will result no change in the status of the beam and thus movement of the mouse will go undetected.
Even though the speed of the axle can be adjusted by gearing as between the ball and the roller, this gearing may result in an overly sensitive mouse that is essentially uncontrollable.
Accordingly there exists a significant limitation on the minimum size of the disks, and therefore on the minimum thickness of the cursor control devices themselves. This limitation makes devices such as those known in the prior art often impractical for use in small, hand-held electronic devices such as cellular telephones and personal digital assistants where size is crucial and little room is available within such devices for cursor control apparatus. Nevertheless, ball-based cursor control devices remain a preferred mechanism for manipulating a graphical user interface.
It is therefore desirable to provide a ball-based cursor control device which provides for cursor movement in two directions that is significantly smaller and thinner than computer mice and trackballs in the known prior art.
These and other objects of the present invention will become apparent to those of ordinary skill in the art in light of the present specifications, drawings, and claims.